A study out Tuesday that questions the stated benefits of breast-feeding is sure to reignite the debate over whether breast is best.

The new research, published in the journal Social Science & Medicine, looked at longitudinal data from three separate populations: 8,237 children, 7,319 siblings and 1,773 sibling pairs where at least one child was breast-fed and at least one child was not. Researchers measured 11 outcomes previously shown to be impacted by breast-feeding: body mass index (BMI); obesity; asthma; hyperactivity; parental attachment; behavior compliance; and achievement in vocabulary, reading recognition, math ability, intelligence and scholastic competence.

When they looked at data across all families, breast-feeding had better outcomes than bottle-feeding in factors like BMI, hyperactivity, math skills, reading recognition, vocabulary word identification, digit recollection, scholastic competence and obesity. However, when the researchers looked just at the siblings who were fed differently, the benefits were not statistically significant. The exception was that breast-fed children were at higher risk for asthma, though it was unclear if those reports were self-generated or actual diagnoses.

It’s well known that moms with higher levels of education, greater income and more flexible daily schedules are more likely to breast-feed their kids. And previous research has shown clear racial and socioeconomic disparities between breast-feeding and non-breast-feeding families. By looking within families, as opposed to across them, the study “[takes] into account all of those characteristics — both measured and unmeasured — that differ by family, such as parental education, household income and race/ethnicity,” Cynthia Colen, lead author and assistant professor of sociology at the Ohio State University, said in a statement.

Colen suggests that the takeaway is to focus on other factors affecting a child’s long-term outlook, like child care, maternity leave, school quality, housing and employment.

A few other studies have also been skeptical of some of the benefit claims of breast-feeding, like weight maintenance. But this recent revelation is unlikely to change any recommendations, and breast-feeding is still highly endorsed by pediatric groups. Multiple studies say breast-feeding is good for the development of the baby, and that it’s health protective for mothers as well. The CDC says it’s “committed to increasing breastfeeding rates throughout the United States and to promoting and supporting optimal breastfeeding practices toward the ultimate goal of improving the public’s health.”